From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752773AbdFOOyr (ORCPT ); Thu, 15 Jun 2017 10:54:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:47534 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752358AbdFOOyq (ORCPT ); Thu, 15 Jun 2017 10:54:46 -0400 Date: Thu, 15 Jun 2017 16:54:43 +0200 From: Petr Mladek To: Sergey Senozhatsky Cc: Sergey Senozhatsky , Steven Rostedt , Andrew Morton , Peter Zijlstra , Aleksey Makarov , Sabrina Dubroca , Sudeep Holla , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] printk/console: Always have a preferred console Message-ID: <20170615145443.GB23337@pathway.suse.cz> References: <1497358444-30736-1-git-send-email-pmladek@suse.com> <1497358444-30736-4-git-send-email-pmladek@suse.com> <20170614091128.GC3011@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170614091128.GC3011@jagdpanzerIV.localdomain> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 2017-06-14 18:11:28, Sergey Senozhatsky wrote: > On (06/13/17 14:54), Petr Mladek wrote: > > > This patch modifies the code that enables the configured consoles. > > It sets the CON_CONSDEV flag also when we register the first > > console. It causes that one of the registered consoles will > > always have CON_CONSDEV flag set. > > hm.... my impression was that we shouldn't set CON_CONSDEV if the > console has no ->device. but then, once again, unregister_console() > does not care and register_console() cares only in one place. so I'm > a bit in doubt. Great catch! It helped me to get even better picture. If I get it correctly, the console driver for /dev/console is found in tty_lookup_driver() by console_device(). Where console_device() skips console drivers without any device. CON_CONSDEV is basically handled only in register_console() and unregister_console(). The driver with this flag is kept at the beginning of the console_drivers list. It causes that console_device() will return the console with this flag. Also it is in sync with the commit cd3a1b8562d28490b33 ("printk: don't prefer unsuited consoles on registration"). It added the check for existing device into the fallback code in console_register() so that console_device() might find a valid one. BTW: The flag CON_CONSDEV first appeared in Linux 2.1.92. It replaced CON_FIRST. Documentation/serial-console.txt was modified so that the last console on the command line will be used for /dev/console instead of the first one. In each case, it seems that CON_CONSDEV is closely related to an existing device and does not make much sense without it. Heh, the handling in unregister_console() looks buggy. Well, it probably does not break anything. The function does not change the order of drivers and console_device() searches the entire list until it finds a console with device. Anyway, it would make sense to clean it as well. Thanks a lot for review. Best Regards, Petr